The driving assistance systems, for example remote controlled speed regulators, enable a human driver to be relieved of some of his or her driving activity on automated systems. These systems are currently widespread on the market, and their functions are increasingly associated with one another to render the vehicle completely autonomous. Such a vehicle type enables the driver to benefit from driving delegation services over all or part of the duration of his or her journey. These driving delegation services can notably be offered when the traffic conditions are dense and the average speed of the vehicle is very low. The manner in which the driver delegates the driving and in which the system hands control to the driver are absolutely essential to the quality of the service provided, and to the dependability of the system. There are procedures for activating and deactivating longitudinal control systems of the vehicle as in the case of a speed regulator or of a distance control system. There are also procedures for activating and deactivating lateral control systems like the line crossing detection systems or lane holding systems. For each of these systems taken separately, it is fairly easy for the driver to know if it is he or she who has control or if it is the automatic system. An autonomous vehicle system of the type to which the invention applies proposes coupling the longitudinal control of the vehicle with the lateral control. The entry into autonomous mode is then achieved by releasing the hands from the steering wheel, then the feet from the pedals (or vice versa), in actions which are not always perfectly synchronized, with the effect of creating situations in which the driver does not know in which state the vehicle is being driven by the automatic systems.
To illustrate the prior state of the art, the document U.S. Pat. No. 8,260,482 discloses a user interface for displaying an internal autonomous driving system state. In manual mode, the interface indicates to the user that the system is ready to operate in autonomous mode based on a variety of information notably comprising a geographic location of the vehicle. The method and the system disclosed do however present a number of problems, including that for the user of precisely knowing the current driving mode at each instant and that for the system of unambiguously managing each of the driving modes.